﻿<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
    <script src="../jquery-1.8.3.min.js"></script>
    <style>
        html,
        body {
            width: 100%;
            height: 100%;
            margin: 0;
            padding: 0;
            overflow: hidden;
        }

        .container {
            width: 100%;
            height: 100%;
            margin: 0;
            padding: 0;
        }
    </style>
</head>
<body>
    <script>
        var RENDERER = {
            SNOW_COUNT: {
                INIT: 100,
                DELTA: 1
            },
            BACKGROUND_COLOR: 'hsl(%h, 50%, %l%)',
            INIT_HUE: 180,
            DELTA_HUE: 0.1,

            init: function () {
                this.setParameters();
                this.reconstructMethod();
                this.createSnow(this.SNOW_COUNT.INIT * this.countRate, true);
                this.render();
            },
            setParameters: function () {
                this.$window = $(window);

                this.$container = $('body');
                this.width = this.$container.width();
                this.height = this.$container.height();
                this.center = {
                    x: this.width / 2,
                    y: this.height / 2
                };
                this.countRate = this.width * this.height / 500 / 500;
                this.canvas = $('<canvas />').attr({
                    width: this.width,
                    height: this.height
                }).appendTo(this.$container).get(0);
                this.context = this.canvas.getContext('2d');

                this.radius = Math.sqrt(this.center.x * this.center.x + this.center.y * this.center.y);
                this.hue = this.INIT_HUE;
                this.snows = [];
            },
            reconstructMethod: function () {
                this.render = this.render.bind(this);
            },
            createSnow: function (count, toRandomize) {
                for (var i = 0; i < count; i++) {
                    this.snows.push(new SNOW(this.width, this.height, this.center, toRandomize));
                }
            },
            render: function () {
                requestAnimationFrame(this.render);

                var gradient = this.context.createRadialGradient(this.center.x, this.center.y, 0, this.center.x, this.center.y, this.radius),
                    backgroundColor = this.BACKGROUND_COLOR.replace('%h', this.hue);

                gradient.addColorStop(0, backgroundColor.replace('%l', 30));
                gradient.addColorStop(0.2, backgroundColor.replace('%l', 20));
                gradient.addColorStop(1, backgroundColor.replace('%l', 5));

                this.context.fillStyle = gradient;
                this.context.fillRect(0, 0, this.width, this.height);

                for (var i = this.snows.length - 1; i >= 0; i--) {
                    if (!this.snows[i].render(this.context)) {
                        this.snows.splice(i, 1);
                    }
                }
                this.hue += this.DELTA_HUE;
                this.hue %= 360;

                this.createSnow(this.SNOW_COUNT.DELTA, false);
            }
        };
        var SNOW = function (width, height, center, toRandomize) {
            this.width = width;
            this.height = height;
            this.center = center;
            this.init(toRandomize);
        };
        SNOW.prototype = {
            RADIUS: 20,
            OFFSET: 4,
            INIT_POSITION_MARGIN: 20,
            COLOR: 'rgba(255, 255, 255, 0.8)',
            TOP_RADIUS: {
                MIN: 1,
                MAX: 3
            },
            SCALE: {
                INIT: 0.04,
                DELTA: 0.01
            },
            DELTA_ROTATE: {
                MIN: -Math.PI / 180 / 2,
                MAX: Math.PI / 180 / 2
            },
            THRESHOLD_TRANSPARENCY: 0.7,
            VELOCITY: {
                MIN: -1,
                MAX: 1
            },
            LINE_WIDTH: 2,
            BLUR: 10,

            init: function (toRandomize) {
                this.setParameters(toRandomize);
                this.createSnow();
                if (
                    navigator.userAgent.match(
                        /(phone|pod|iPhone|iPod|ios|Android|Mobile|BlackBerry|IEMobile|MQQBrowser|JUC|Fennec|wOSBrowser|BrowserNG|WebOS|Symbian|Windows Phone)/i
                    )
                ) {
                    var box = document.querySelectorAll('.box')[0];
                    box.style.left = '42%';
                }
            },
            setParameters: function (toRandomize) {
                if (!this.canvas) {
                    this.radius = this.RADIUS + this.TOP_RADIUS.MAX * 2 + this.LINE_WIDTH;
                    this.length = this.radius * 2;
                    this.canvas = $('<canvas />').attr({
                        width: this.length,
                        height: this.length
                    }).get(0);
                    this.context = this.canvas.getContext('2d');
                }
                this.topRadius = this.getRandomValue(this.TOP_RADIUS);

                var theta = Math.PI * 2 * Math.random();

                this.x = this.center.x + this.INIT_POSITION_MARGIN * Math.cos(theta);
                this.y = this.center.y + this.INIT_POSITION_MARGIN * Math.sin(theta);
                this.vx = this.getRandomValue(this.VELOCITY);
                this.vy = this.getRandomValue(this.VELOCITY);

                this.deltaRotate = this.getRandomValue(this.DELTA_ROTATE);
                this.scale = this.SCALE.INIT;
                this.deltaScale = 1 + this.SCALE.DELTA * 500 / Math.max(this.width, this.height);
                this.rotate = 0;

                if (toRandomize) {
                    for (var i = 0, count = Math.random() * 1000; i < count; i++) {
                        this.x += this.vx;
                        this.y += this.vy;
                        this.scale *= this.deltaScale;
                        this.rotate += this.deltaRotate;
                    }
                }
            },
            getRandomValue: function (range) {
                return range.MIN + (range.MAX - range.MIN) * Math.random();
            },
            createSnow: function () {
                this.context.clearRect(0, 0, this.length, this.length);

                this.context.save();
                this.context.beginPath();
                this.context.translate(this.radius, this.radius);
                this.context.strokeStyle = this.COLOR;
                this.context.lineWidth = this.LINE_WIDTH;
                this.context.shadowColor = this.COLOR;
                this.context.shadowBlur = this.BLUR;

                var angle60 = Math.PI / 180 * 60,
                    sin60 = Math.sin(angle60),
                    cos60 = Math.cos(angle60),
                    threshold = Math.random() * this.RADIUS / this.OFFSET | 0,
                    rate = 0.5 + Math.random() * 0.5,
                    offsetY = this.OFFSET * Math.random() * 2,
                    offsetCount = this.RADIUS / this.OFFSET;

                for (var i = 0; i < 6; i++) {
                    this.context.save();
                    this.context.rotate(angle60 * i);

                    for (var j = 0; j <= threshold; j++) {
                        var y = -this.OFFSET * j;

                        this.context.moveTo(0, y);
                        this.context.lineTo(y * sin60, y * cos60);
                    }
                    for (var j = threshold; j < offsetCount; j++) {
                        var y = -this.OFFSET * j,
                            x = j * (offsetCount - j + 1) * rate;

                        this.context.moveTo(x, y - offsetY);
                        this.context.lineTo(0, y);
                        this.context.lineTo(-x, y - offsetY);
                    }
                    this.context.moveTo(0, 0);
                    this.context.lineTo(0, -this.RADIUS);
                    this.context.arc(0, -this.RADIUS - this.topRadius, this.topRadius, Math.PI / 2, Math.PI * 2.5, false);
                    this.context.restore();
                }
                this.context.stroke();
                this.context.restore();
            },
            render: function (context) {
                context.save();

                if (this.scale > this.THRESHOLD_TRANSPARENCY) {
                    context.globalAlpha = Math.max(0, (1 - this.scale) / (1 - this.THRESHOLD_TRANSPARENCY));

                    if (this.scale > 1 || this.x < -this.radius || this.x > this.width + this.radius || this.y < -this.radius || this.y > this.height + this.radius) {
                        context.restore();
                        return false;
                    }
                }
                context.translate(this.x, this.y);
                context.rotate(this.rotate);
                context.scale(this.scale, this.scale);
                context.drawImage(this.canvas, -this.radius, -this.radius);
                context.restore();

                this.x += this.vx;
                this.y += this.vy;
                this.scale *= this.deltaScale;
                this.rotate += this.deltaRotate;
                return true;
            }
        };

        $(function () {
            RENDERER.init();
        });
    </script>
</body>
</html>
